Separation of plant fibers



Patented Apr. 29, 1941 Clyde R. Faullrcnder, Ames, Iowa, assignor to Milkweed Products Development Corporation, Chicago, 11]., a corporation of Illinois No Drawing. Application May 25, 1939,

Serial No. 275,699

3 Claims.

A number of well known plants, such as the common milkweed, the hemp, the sunflower, and indeed most plants having stalks characterized by the lack of a strong woody supporting structure, possess a prominent layer of bast fibers which impart rigidity to the stalk. The bast fibers of many plants have considerable commercial importance, and others show great promise of attaining importancein the near future. I wish especially to stress the importance of the common milkweed, the utilization of whose many valuable properties has been made the subject of numerous patent applications by myself and my associates.

The milkweed stalk is composed of successive layers of bark, bast fibers, woody fibers, inner fiber, and pith cells. The only important layers are the bast fiber layer and the woody layer- The bast fibers comprise about 22 per cent of the stalk The woody fibers comprise about 70 per cent of the stalk. Milkweed bast fibers consist of approximately 92% per cent alpha-cellulose and are therefore suitable for use in the manufacture o1 rayon, photographic films, high grade paper, and in other manufactures requiring highly purifiedcellulose. Milkweed woodfibers are suitable ior the manufacture of paper and can be converted into plastics.

It is apparent that the bast fibers and the woody fibers differ materially in their properties and uses, and require different treatments. The

.difiiculty of separating these fibers has been one of the deterrents to their commercial utilization.

One of the objects of my invention is to provide a practical method of separating the bast fibers from the woody fibers of plants.

Another object of my invention is the production of crudealpha-cellulose from'the common milkweed.

Other objects and advantages of my invention will become apparent upon reading the following specification.

In the practice of my invention I find it necessary to bring the stalks of the milkweed to a moisture content ranging between and per cent. The separation of the bast fibers from the woody fibers is most easily accomplished in this range of moisture content. The separation is performed by subjecting the stalks to a breaking or bending action. The highly flexible bast fibers, which are highly flexible at the indicated stalk moisture content, are not affected by such treatment, but the comparatively friable woody fiber breaks into small fragments which are loosened from the bast fibers by the violent bending to which they are subjected.

, tent of the stalks is maintained between 10 and ine flexibility of the bast fibers is due to their relatively great legnth as compared to their diameter. They are one-quarter to three-quarters of an inch in length, but only 0.001 to 0.003 inch in diameter. In addition, they are branched and entangled with each other, forming the so-called fiber bundles which are of great flexibility and tensile strength. The woody fibers, contrastingly, are very short unbranched fibers lacking in longitudinal cohesiveness although they cohere well laterally. They are therefore quite friable, brittle, and readily comminuted.

' In preparation for the separation of the bast fibers from the woody, I reduce the milkweed stalks to pieces from two to four inches in length by means of-breaking rolls. The pieces are then subjected to still more violent breaking roll treatment which produces a combined shredding, breaking, and bending action. The i'riable woody fibers are thereby broken into small fragments which are torn from the best fibers to which they are only loosely attached when the moisture con- 20 per cent.

After the stalks have been broken up by the violent mechanical treatment to which I subject them, the relatively long bast fiber bundles are separated from the finely divided woody fibers and short broken lengths of bast fibers by screening on a one inch screen. The material retained upon the screen is the bulk of the substantially pure crude bast fiber. The material which passes through the screen consists of the a woody fibers, short length of bast fibers, and

short unseparated pieces of stalk. It must be subjected to another beating and bendingtreatment to separate the small quantity of bast fiber cohering to the woody fibers. This is accomplished by passing it through a swing hammer-mill having a plate with one inch openings.

The crude bast fiber can easily be purified by means of a process disclosed in one of my copending applications to produce highly pure alpha-cellulose, which has innumerable uses in the new highly developed chemical cellulose industry. The crude bast fiber is suitable for the production of paper, without further purification, except the usual bleaching. Milkweed bast fiber is especially notable for the ease with which it may be bleached.

Having described my invention in such detail as will enable those skilled in the art to practice' the process, I claim:

1. The method of separating plant fibers of the class described comprising adjusting the moisture content of natural stalks to be treated to between ten and twenty per cent, breaking the stalks into short pieces, subjecting the pieces while kept at the same moisture content to violent breaking action to comminute the woody fibers of the stalk and to loosen the fragments thereof from the bast fibers, and screening the bast fibers from the woody fiber.

2. The method of separating plant fibers of the class described comprising adjusting the moisture content of the stalks to be treated to between ten and. twenty per cent, subjecting the stalks to violent breaking action to comminute the woody fibers of the stalk and to loosen the fragments thereof from the bast fibers, screening the bulk of the crude bast fibers from the woody fibers, subjecting the woody fibers to a violent beating and breaking action, to. separate the small quantity of bast fibers remaining attached to the woody fibers, screening the bast fibers from the resulting product, and combining the best fibers thus obtained with the crude bast fibers from the previous screening.

3. The method of separating plant fibers of the class described comprising adjusting the moisture content of the stalks to be treated to between ten and twenty per cent, subjecting the stalks to violent breaking action to comminute the woody fibers of the stalk and to loosen the fragment; thereof from the bast fibers, screening the bulk of the crude bast fibers from the woody fibers, subjecting the woody fibers to a violent beating and breaking action, to separate the small quantity of bast fibers remaining attached to the woody fibers, screening the bast fibers from the resulting product, combinin the best fibers thus obtained with the crude bast fibers from the previous screening, and rescreening the woody fiber to separate bark and chaff therefrom.

CLYDE R. FAULKENDER. 

